The Eocene to Oligocene Nisai Formation in the Khuzhobai Section, Pishin Belt (Balochistan, SW Pakistan), was investigated to determine its microfacies, depositional environments, and burial history. A visual estimation technique is used to quantify different allochemical constituents and discriminate microfacies. A total of eight microfacies were identified in the limestone unit of the Nisai Formation through detailed microfacies analysis. The identified microfacies represent deposition of the Nisai Formation in a carbonate ramp setting, including inner, middle, and outer ramp environments. The lagoonal facies in the inner ramp setting is characterized by imperforate foraminifera such as miliolids and Alveolina and abundant coralline red algae. The middle ramp facies are characterized by abundant Nummulites, Assilina, and coralline red algae, together with a rare to sparse amount of shallow marine fauna including gastropods, echinoderms, and ostracods. The outer ramp facies is characterized by planktonic foraminifera and mudstone depositional texture. Based on the comparison of larger benthic foraminifera (LBF) assemblages, microfacies characteristics, and mixing of faunas in the middle ramp setting, a mixed carbonate-siliciclastic, storm-dominated homoclinal ramp depositional model is suggested for the Nisai Formation. The studied formation has been altered by various diagenetic processes, which occurred in different diagenetic environments, including the marine, meteoric-phreatic, and burial environments. The early marine diagenetic environment is indicated by features such as burrowing, micritization, and grain packing, whereas the meteoric-phreatic environment is evidenced by processes like inversion neomorphism, dissolution, drusy and granular mosaic calcite cements, as well as the presence of pendant and meniscus cements. The burial phase is evident from the aggrading neomorphism, further mechanical grains packing, fracturing, and stylolitization, followed by a minor phase of uplift and unroofing. Visible secondary porosity in the Nisai Formation has been significantly enhanced by dissolution within the meteoric-phreatic diagenetic environment.